1. Field of the Invention
The present invention relates to the field of reducing nitrogen oxide emission from internal combustion engines and turbines, and more particularly to a novel means and method for conducting a feed mixture flow from a preheater assembly to a fully insulated burner having an insulated inner burner supplying gases from a portion or part of the main engine fuel whether it be gaseous or liquid to an insulated outer burner.
2. Brief Description of the Prior Art
It is well known that nitrogen oxides (NO.sub.x) form at the high temperatures normally associated with combustion processes and that operating an engine at lean conditions with excess air lowers temperature and, therefore, decreases NO.sub.x. However, decades of engine and turbine studies have shown that lean combustion limits are above those where NO.sub.x emissions are below specified goals. Natural gas and gasoline are examples where lean combustion has been pushed to its limit and where it has been found that hydrogen addition increases this limit to where NO.sub.x output is acceptably low. However, means to obtain hydrogen for this purpose are beset with problems.
Problems and difficulties have been encountered when the supply of hydrogen is provided by materials carried in a separate tank which can be extremely heavy and requires pressurization. As examples, methanol, hydrogen or ammonium nitrate can provide or produce hydrogen when added to an engine combustor. However, these take the place of the fuel and so reduce the volumetric storage capacity which lowers overall performance, and results in complications through use of secondary materials. Hydrogen stored in the pressurized container which holds methane (Hythane) can also be used, but this causes about 0.75 percent reduced engine range for each percent hydrogen used because of its very low energy content on a volumetric basis, and also requires special means to enable safe storage of hydrogen.
The present invention teaches the use of an underoxidized burner using the main fuel to obtain hydrogen.
Previous attempts have been made to improve the underoxidized burner disclosed in the applicants' two previous patent applications by pre-mixing fuel and air, pre-heating the fuel-air feed by heat exchange with the burner products, and affecting circulation of the burning products. Such prior attempts have been successful in reducing nitrogen oxide emission. Thus, the two stage burner described in the first disclosure utilizes technology to effect chemical equilibration with air-fuel formulations containing a great excess of fuel and a second stage in the prior disclosures utilizes related technology to attempt equilibration between the products of the first stage and excess air.
Conventional burners operate air rich and react in roughly two stages. The first stage includes regions with air-fuel ratios near stoichiometric wherein high temperatures occur that induce initiating undesired chemical reaction with the fuel. Such temperatures result in elevated concentrations of NO.sub.x. A second stage operates air rich to achieve final overall air-fuel ratio. Its temperature is lower but not sufficiently low that NO.sub.x cannot form, and this stage generally does not remove NO.sub.x which has been formed in the first stage. The overall result is that NO.sub.x formed in both stages appears in the burner exhaust.
In the second previous patent application mentioned above, technology is disclosed for attaining chemical equilibration between air and a large excess of fuel in an underoxidized burner through a process whereby the air-fuel mixture undergoes certain rapid flow reversals. This technology results in equilibration at a reasonably high temperature without resulting in formation of NO.sub.x since its excessive fuel concentration preferentially causes reaction between air and fuel instead of air and N.sub.3 to form NO.sub.2.
It has been found that the technology of U.S. Pat. Nos. 5,207,185 and 5,299,536 results in products that are easily combusted with further air. As a consequence, a combustor with excess air for powering engines which products virtually zero NO.sub.x can be achieved by a related two-stage process. The first stage comprises a fuel-rich burner of the type taught in these co-patents. The second stage uses similar technology but operates air rich. Products from the first stage and the excess air needed to attain the final air-fuel mixture are introduced into the second stage. In this stage, a mixture of the latter air and latter products undergoes the same rapid flow reversals taught by the technology of the co-patents, which result in their rapid chemical equilibration. In view of the improved reactivity of the fuel products obtained from the underoxidized burner, the induced flow reversals, and the relatively high concentration of hydrogen, equilibration can be induced in the second stage at a higher ration of air-fuel than normally used. This results in very low temperatures where NO.sub.x formation is very low.
The technology of the co-patents results in an underoxidized burner replacing the customary near-stoichiometric regions in the first stage of a burner. While the latter produces NO.sub.x that eventually appears in the exhaust, NO.sub.x cannot form in the very fuel rich underoxidized burner. It equilibrates instead to easily combustible CO and H.sub.2, and very minor amounts of undecomposed fuel. As a consequence, injecting a mix of such products and the air needed to attain the desired overall air-fuel ration into a second stage burner which incorporates means to achieve the same rapid flow reversals taught by the co-patents, results in rapid chemical equilibration. These factors, aided by the relatively high concentration of H.sub.2, permits stable combustion at extraordinarily lean air/fuel ration with relatively low temperature where NO.sub.x does not form.
Therefore, a long-standing need has existed to provide novel means and methods for accomplishing a technology breakthrough for a simple means of producing hydrogen from fuel in a simple fully insulated burner without the catalyst and without a special pressurized hydrogen or related storage means heretofore normally considered required and whereby improved results are gained employing first and second stages which are virtually NO.sub.x free, as is the overall combustor, leading to a no-NO.sub.x burner.